Chandogya Upanishad...

In the beginning was only Being,
One without a second.
Out of himself he brought forth the cosmos
And entered into everything in it.
There is nothing that does not come from him.
Of everything he is the innermost Self.
He is the truth; he is the Self supreme.
You are that, Shvetaketu; you are that.

Merge in the sea and become one with it,
Forgetting they were ever separate streams,
So do all creatures lose their separateness
When they merge at last into pure Being.
There is nothing that does not come from him.
Of everything he is the innermost Self.
He is the truth; he is the Self supreme.
You are that, Shvetaketu; you are that!